# Very high engine rpm all of a sudden on 98 tahoe. what gives? **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [February 16, 2014, 5:50am UTC](https://community.cartalk.com/t/very-high-engine-rpm-all-of-a-sudden-on-98-tahoe-what-gives/83740 "2014-02-16T05:50:36Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![grizz](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/grizz/32/2597_2.png) [@grizz](https://community.cartalk.com/u/grizz)\ **Post date:** [February 16, 2014, 5:50am UTC](https://community.cartalk.com/t/very-high-engine-rpm-all-of-a-sudden-on-98-tahoe-what-gives/83740/1 "2014-02-16T05:50:36Z")
…it happened as I was stopped at a traffic light. without warning it just revved up as though I punched the gas pedal, which I didn’t. had my foot on the brakes but it still wanted to fly! I dumped it into park and it really howled! I shut off the engine, started it back up and everything was fine! what the heck caused this and what needs fixed? thanks for any and all help. ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [February 16, 2014, 6:07am UTC](https://community.cartalk.com/t/very-high-engine-rpm-all-of-a-sudden-on-98-tahoe-what-gives/83740/2 "2014-02-16T06:07:51Z")
The Idle Air Control valve went wide open. I’d replace it before you end up rear-ending someone when the IAC decides to do it again. Tester ---
**Author:** ![grizz](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/grizz/32/2597_2.png) [@grizz](https://community.cartalk.com/u/grizz)\ **Post date:** [February 16, 2014, 7:03pm UTC](https://community.cartalk.com/t/very-high-engine-rpm-all-of-a-sudden-on-98-tahoe-what-gives/83740/3 "2014-02-16T19:03:41Z")
…thanks for the good advice. any idea what the fix would cost? thanks. ---
**Author:** ![VDCdriver](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/vdcdriver/32/48514_2.png) [@VDCdriver](https://community.cartalk.com/u/VDCdriver)\ **Post date:** [February 16, 2014, 7:40pm UTC](https://community.cartalk.com/t/very-high-engine-rpm-all-of-a-sudden-on-98-tahoe-what-gives/83740/4 "2014-02-16T19:40:20Z")
Depending on where you live and on whether a genuine GM IAC or an aftermarket IAC is used, I think that the cost (parts + labor) could range anywhere from ~$120-$220. ---
**Author:** ![grizz](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/grizz/32/2597_2.png) [@grizz](https://community.cartalk.com/u/grizz)\ **Post date:** [February 18, 2014, 5:54pm UTC](https://community.cartalk.com/t/very-high-engine-rpm-all-of-a-sudden-on-98-tahoe-what-gives/83740/5 "2014-02-18T17:54:18Z")
thanks all for the responses. I wanted to ask also, is there any other part failure that would cause my problem or is the IAC pretty much the most likely failure. thanks again ---
**Author:** ![grizz](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/grizz/32/2597_2.png) [@grizz](https://community.cartalk.com/u/grizz)\ **Post date:** [February 19, 2014, 12:52am UTC](https://community.cartalk.com/t/very-high-engine-rpm-all-of-a-sudden-on-98-tahoe-what-gives/83740/6 "2014-02-19T00:52:20Z")
![](http://i213.photobucket.com/albums/cc158/katek1304/popcorn_zps1a55b164.gif) ---
**Author:** ![Big\_Marc](https://avatars.discourse-cdn.com/v4/letter/b/9d8465/32.png) [@Big\_Marc](https://community.cartalk.com/u/Big_Marc)\ **Post date:** [February 19, 2014, 3:17am UTC](https://community.cartalk.com/t/very-high-engine-rpm-all-of-a-sudden-on-98-tahoe-what-gives/83740/7 "2014-02-19T03:17:19Z")
same thing happened on my 300M it just wanted to pull away from me at a light put the car in nuetrel and the rpm’s would climb to 1500 from 700. the new iac s;oved that problem ---
**Author:** ![cigroller](https://avatars.discourse-cdn.com/v4/letter/c/c68b51/32.png) [@cigroller](https://community.cartalk.com/u/cigroller)\ **Post date:** [February 19, 2014, 7:13am UTC](https://community.cartalk.com/t/very-high-engine-rpm-all-of-a-sudden-on-98-tahoe-what-gives/83740/8 "2014-02-19T07:13:17Z")
The only other things that stand any chance of doing this are things like the throttle getting stuck open or exactly the right sized vacuum leak. Neither one of those could apply given that it goes back to normal if you shut it down and restart it. So I’d put the IAC odds at about 99%. However - the other 1% is about voltage supply for the IAC. The IAC only works by wires connected to the PCM which actually regulates it. There is always a chance that the problem is on the control side.